Measuring system



DEFLECTION 'PER CENT J. B. SHERMAN 2,215,197

MEASURING SYSTEM Original Filed NOV. 9, 193 3 Sheets-Sheet l kHAXAT/UN I FREQUENCY CAT/100E use/mm FIXED VOLTAGE o/sm/M- "EU/HER ova.

VAR/ABLE osclzurok AMPLIFIER-P- INATING AND AMPUF/ER p pp NETWORK TER K li AMflifi/ER VERTICAL VAR/A3: DETECTOR POWER *IAPPARATl/Sio- HER AMPLIFIER ARC. 0501mm? AND UNDER I FILTER AND LRF/LTER TEST :o-RQAMPL DEFECT/0N (l/NEAROR CONTROL g wean/mum) FREOUENCY- CYCL E5 PER SECOND INVENTOR. JESSE B. SHERMAN ATTORNEY.

pt. 17. 1940. J. B. SHERMAN 2,215,197

MEASURING SYSTEM Original Filed Nov. 9, i93 3 Sheets-Sheet 3 Q v 9 3 CYCZES PER SECOND CYC'ZES PER SECOND Q Q Q a CYCLES PER SECOND CYCZES PER SECOND INVENTOR.

JESS B. SHERMAN ATTORNEY.

Patented Sept. 17, 1940 UNITED STATES PATENT OFFICE MEASURING SYSTEM Jesse B. Sherman, New York, N. Y., asslgnor to Radio Corporation of America, a corporation of Delaware 1939, Serial No. 266,747

11 Claims.

This invention relates to measuring systems and more particularly to the method of and means for rapidly determining the frequency response characteristics of electrical networks, as well as vibratory or oscillatory mechanical systems, and is a division of U. S. Patent #2,1'75,001, issued October 3, 1939.

It is sometimes desirable or necessary in the study of mechanical and electrical vibratory systems and frequency response systems to know the relationship between the response amplitude of one or more of the parameters of the system as a function of the frequency of the driving force applied thereto and to show this relationship visually in graphic form with the ordinate values representing the amplitude of response and the abscissae representing the values of the applied frequency. In measuring systems which have previously been used the apparatus for and method of obtaining such characteristics were either quite complicated and required more or less elaborate set-ups of an extensive nature, or were relatively simple and required separate and individual tests for each point on the curve.

The point-by-point method which has been used in the preparation of frequency response characteristics of frequency responsive systems is not entirely satisfactory inasmuch as a great number of points must be plotted particularly where the apparatus varies rapidly in-response with respect to the applied frequency. In an acoustic device which responds to an applied frequency, such as a loud speaker, for instance, the apparatus inherently displays rapid rates of change with respect to the applied frequency and as a result, to produce an accurate curve representing the frequency response characteristics of the device the number of points required becomes prohibitive for practical work.

The present invention, therefore, more specifically relates to a system whereby the frequency response characteristics of a frequency responsive system or device may be determined and presented in the form of a curve or graph through the use of a cathode ray tube which is provided with a fluorescent or viewing screen, the characteristic curve of the particular apparatus in ques tion being displayed on the viewing end of a cathode ray tube. The present invention is a continuation in part of application Serial No. 161,795 of Jesse B. Sherman, filed August 31, 1937.

In the present invention wherein it is possible to display the characteristics of a frequency response apparatus on the viewing screen of a cathode ray tube, it is desirable that the abscissae.

which represent the applied frequency, vary logarithmically in order that more accurate determinations of the frequency response characteristics may be had in the lower frequencies. The horizontal movement of the beam in the cathode ray tube is repeated deflected automatically by reason of a relaxation generator and its action on a beat frequency generator, the beat frequency generator including a variable oscillator and a fixed oscillator. In some instances, however, it is desirable to expand portions of the abscissae with respect to frequency in order that the frequency response characteristics of the apparatus in question may be more fully ascertained and examined within a particular desired range of frequencies.

It is also desirable in a system such as that shown and described to render the vertical deflection of the cathode ray beam ineffective during the time that the cathode ray beam is horizontally returned across the screen prior to the presentation of a subsequent characteristic curve. It is also desirable in such a system to provide means whereby the cathode ray beam and the variable oscillator may be stopped at a particular point in the cycle of operation in order that adjustments may be made to properly position the curve produced on the field of the viewing screen of the cathode ray tube and in order that the usual zero adjustment to the variable oscillator of the beat frequency generator may be made.

It is therefore one purpose of the present invention to provide means whereby the frequency response characteristics of a frequency responsive system or device may be ascertained, and whereby a curve of this characteristic be presented on the viewing screen of a cathode ray tube.

It is a further purpose of the prevent invention to provide means whereby the abscissae of the produced curve will represent the applied frequency, the abscissae varying according to a log arithmic function of the applied frequencies.

It is still another purpose of the present invention to provide means whereby various portions of the abscissae may be expanded with respect to frequency in order that the frequency response characteristics of the device in question may be more fully and more accurately determined over the particular expanded portion of the curve.

A further purpose of the present invention resides in the provision of means whereby the frequency response of the particular apparatus under test, that is. the ordinate values of the characteristic curve, may be applied to the vertical deflecting plates of a cathode ray tube, with still further means whereby the degree of vertical deflection may vary linearly or logarithmically with respect to the frequency response.

It is still another purpose of the present invention to provide means whereby the vertical deflection of the cathode ray beam, which repre sents the frequency response of the particular apparatus, be made ineilective during those periods when the cathode ray beam is returned to the initial starting point prior to the production of a subsequent characteristic curve.

It is still another purpose of the present invention to provide means whereby the movement of the cathode ray beam may be entirely stopped in order to facilitate the zero setting of the beam whereby the curve on the viewing screen of the cathode ray tube may be properly positioned and in order that the usual zero adjustment to the variable oscillator of the beat frequency generator may be made.

Still another purpose of the present invention resides in the provision of means whereby all alternating current components of the current or voltage derived from the particular apparatus in question may be eliminated in order that the voltages which are ultimately applied to the vertical deflection plates may be free from any superimposed alternating currents and whereby these voltages will vary directly or logarithmically in proportion to the frequency response of the particular apparatus in question.

It is another purpose of the present invention to provide means whereby the movement of the cathode ray beam across the viewing screen will be uniform with respect to time, yet will move logarithmically with respect to the applied frequency.

Other purposes and advantages of the present invention will become more apparent to those skilled in the art by a reading of the following more detailed description, particularly when considered in connection with the drawings wherein corresponding parts are represented by corresponding reference characters, and wherein:

Figure 1 represents a block diagram of the apparatus used in the present invention,

Figure 2 shows a system constructed in accordance with the present invention,

Figure 3 shows a plurality of curves indicating the percent of horizontal deflection of the cathode ray beam as a function of the applied frequency, the curves representing both the logarithmic response and the expanded response. Figures 4, 5, 6 and '7 represent typical curves which may be presented in the viewing screen of the cathode ray tube and illustrate the effect of the expansion of particular portions of the produced curve.

The present invention is shown schematically in the block diagram of Figure 1 and represents the elements which are used to produce a system in accordance with the present invention. A relaxation oscillator I0 is provided which may be adjustable in order that the periodicity of the oscillations may be controlled. The range of the periodicity is preferably chosen, for example, to lie within the limits of 10 seconds and one minute. This apparatus determines the length of time required for the cathode ray beam to produce the frequency response characteristic curve of the particular apparatus tested. The output from the relaxation oscillator is supplied to an automatic frequency control system l2, which controls a variable oscillator M which, together with a fixed oscillator l6, supplies a beat frequency which varies from to 15,000 cycles per second, for example. These frequenciesare detected and are subjected to a low-pass filter II and the resulting cyclically varying oscillations are applied to a power amplifier 20 which in turn supplies the cyclically varying frequencies to the particular apparatus under test.

The cyclically varying frequencies which are derived from the detector and low-pass filter l8 are also applied to a voltage amplifier 22 and the output from this amplifier is led to a frequency discriminating network 24 for the purpose of producing the desired potentials for horizontally deflecting the cathode ray beam. This frequency discriminating network includes a series of parallel resistances and condensers for the purpose of causing the beam to be deflected logarithmically with respect to the applied frequency. The frequency discriminating network also includes means whereby various frequency bands may be expanded, the bands being selectable at will by the operation of a selector switch. The output from the frequency discriminating network is applied to a rectifier and filter system 26, which in turn supplies energy to a direct current amplifier 28, the output of which is connected to the horizontal deflecting plates of the cathode ray tube 30.

The energy from the particular apparatus under test is applied to a system which comprises an alternating current amplifier, a rectifier, a filter network and a direct current amplifier, all of which are represented by the rectangle 32. This portion of the system is provided with means whereby a linear or logarithmic response may be produced in order that the vertical deflections on the screen of the cathode ray tube may vary in direct proportions to the output of the device tested or may vary logarithmically with respect to the output of the device. The output from this system is supplied to a vertical amplifier and deflection control system 34. This system is also supplied with impulses from the relaxation oscillator l0 and includes means whereby the vertical amplifier is made ineflective during the periods when the cathode ray beam is horizontally returned to the initial starting point. The output of this system is applied to the vertical deflecting plates of the cathode ray tube 30.

Figure 2 shows the actual circuits used in portions of the entire system. The remaining portions which are old and well knownin the art are shown in block diagram in order that the complete system may be materially simplified.

The relaxation oscillator employs a tube 36 which is a gas discharge tube and which may be, for example, a type 885 gas discharge tri ode. A condenser 38 which is of relatively large capacity is provided, one terminal of which is grounded and the other terminal of which is connected to one end of tapped resistor 40. The various taps along the resistor 40 may be selectively connected to a switch arm 42 which in turn is connected to a negative source of voltage 44 when the switch arm 46 is in the lower or automatic position. This provides a charging circuit for the condenser 38, the rate of charge being determined by the amount of the resistance 40 which is included in series therewith. The cathode or electron emitter element of the tube 36 is connected to a point between the condenser 38 and a resistance 40 and the anode of the tube 36 is connected to ground by wayof a relatively highrethe switch arm 48 and when all of the switch arms are in the lower position the relaxation oscillator operates automatically, whereas, when the switch arms are all in the upper position manual operation of the oscillator may be accomplished.

The relaxation oscillator I 0 produces a sawtooth volta'ge the frequency of which is determined by the amount of resistance 40 which is included in series with the condenser 38 and which is determined by the position of the switch arm 42. The condenser 38 charges according to an exponential characteristic and when a predetermined charge has accumulated on the condenser 38, the condenser will discharge through the tube 38, the amount of charge necessary to produce a break-down of the tube 38 being controlled by the bias applied to the control electrode of the tube.

The output of the relaxation oscillator is applied to the automatic frequency control system I2 which may be of a type well known in the art and which comprises a tube 82 which may, for example, be of the type generally known as a 956. Means are provided whereby appropriate voltages may be applied to the automatic frequency control system i2.

The automatic frequency control system is connected to the grid end of the tank coil of the variable oscillator I4 and the output from the variable oscillator I4, together with the output from a fixed oscillator I8, are applied to the detector and low-pass filter system I8. The variable oscillator, together with the fixed oscillator produce a beat frequency which cyclically varies between the limits of 20 cycles per second and 15,000 cycles per second. The period of each cycle is controlled by the frequency of the relaxation oscillator.

The cyclically varying logarithmic frequency variations from the detector and low-pass filter system I8 are applied to a power amplifier 20 from which the energy is derived which is applied to the particular apparatus under test.

The varying frequency oscillations as amplified by the power amplifier 20 are also applied to the voltage amplifier 22 which comprises a tube 84 which may, for example, be a triode of the type 605. A source of potential 88 is provided for maintaining the proper potential on the anode of the tube 84. Connected to the anode of the tube 84 is a switch arm I8 which may be selectively placed in contact with any of the switch terminals I2, I4, I8 or I8.

The switch terminals I2, 14, I8 and I8 are connected to the frequency discriminating network 24 which comprises a resistance 88, a condenser 82 'and a plurality of parallel resistances and condensers. The switch terminal I2 is conthis network is to produce a voltage which varies logarithmically with respect to the applied frequency in order that the deflection of the cathode ray beam may vary in a logarithmic manner with respect to the frequency applied to the discriminating network and to the particular apparatus under test.

A plurality of condensers 84, 88 and 88 are also provided, one terminal of each of which is connected respectively to the switch contacts I4, I8 and I8. The other terminals of the condenser 84, 88 and 88 are connected together and are in turn connected to the end 83 of the resistance 80. The purpose of these condensers is to produce expansion with respect to frequency over a particular frequency range of the frequency applied to the apparatus under test, and the particular range expanded is determined by the size of the particular condenser which is connected in series with the resistance 80. By positioning the switch arm I0 on any one of the switch terminals I4, I8 or I8, a horizontal expansion of the characteristic curve of the particular apparatus under test may be accomplished, the frequency range of the expanded portion being determined by the value of the resistance 88 and the particular condenser connected in series therewith.

A voltage is produced across the resistance 88 of the frequency discriminating network 24, and this voltage is applied to the rectifier and filter system 28 which comprises a duo-diode tube 98 which may be of the type 6H6 and a resistor 92 and a condenser 94. The tube 90 operates as a half-wave rectifier and the resistor and condenser combination 92, 94 operates as a filter.

The rectified and filtered output from the frequency discriminating network and amplified system appears across the resistance 92 and this potential is applied to the control electrode of tube 98 which constitutes the direct current,

amplifier system 28. The tube 98 may, for instance, be of the type 6J7 which is a triple-grid amplifier. A source of current 98 is provided whereby the electrodes of the tube 98 may be maintained at proper operating potentials. The output from' the amplifier 28 is applied to the deflecting plates I08 of the cathode ray tube 30 in order that the cathode ray beam may be deflected in a horizontal direction.

The output from the power amplifier 28, which is a cyclically varying oscillation, is applied to the particular apparatus under test which may be any electrical frequency responsive system or any mechanical frequency responsive system. Voltages which are derived from the particular apparatus under test in response to the applied frequencies are impressed upon the input terminals 3i of the system represented by the rectangle 32. This system includes alinear alternating current amplifier since the output from the apparatus under test will be alternating in nature and the output from the amplifier is rectified and filtered and finally amplified by a direct current amplifier. The direct current amplifier may be provided with means whereby the amplification may be linear or logarithmic as explained above.

The output from the direct current amplifier is applied to an additional amplifier stage which comprises a tube I02 which may be, for example, of the type 6J7. A source of positive potential I 04 is provided for maintaining the anode and second control .electrode of the tube at proper operating potentials and a small condenser I08 is that the output oi the tube I02 will contain no alternating current but only direct current or vol- I A tag'e which varies in intensity in accordance with the frequency response oi. the particular apparatus tested. The anode of tube I02 is connected to the vertical deflecting plates H0 01 the cathode ray tube 30. p

It may be seen, therefore, that the beam of the cathode ray tube 30 may be caused to be deflected horizontally as a function of the frequency applied to the particular apparatus under test and that the deflection may be either directly logarithmic or may have particular portions of the abscissae expanded with respect to frequency. Also, the beam may be deflected vertically in accordance with the frequency response of the particular apparatus under test.

The length of time required for the cathode ray beam to make one complete horizontal deflection is determined by the setting of the selector switch 2 which controls the amount of resistance which is included in series with the condenser 38, and at the end of the deflection time the cathode ray beam is returned for a subsequent deflection at the same instant that the condenser 38 is discharged through the tube 36. During this return it is desirable that vertical deflection of the cathode ray beam be prevented in order that the return trace 0! the beam will not cause a confusing curve to be superimposed upon the characteristic curve of the particular apparatus being tested.

In order to prevent the beam from being deflected vertically during its return period horizontally, a deflection control system is provided which comprises the tubes I08 and I09 which may be triodes of the type 6J5, for example. The anode of tube 36 of the relaxation oscillator I0 is connected to the control grid I I2 of tube I08 and the anode H3 0! this tube is connected to the control grid I of tube I09. The control grid' H4 controls the amount of current which is permitted to pass to the anode H5 of tube I09 and this anode is connected to the connection between the anode of tube I02 and the vertical deflecting plates I I0. It is desirable that the vertical beam deflection be controlled after the input from the apparatus under test has been amplified and rectified in order that the switch will not aifect the time constant of the filters contained within the circuit represented by the rectangle 32.

The deflection control system for preventing vertical deflection of the cathode ray beam during horizontal return of the beam to an initial starting point operates in the following manner: During the charging period of the condenser 38 there is no potential applied to the anode of tube 36. Accordingly no potential is applied to the control grid II! of the tube I08 and this electrode is at zero bias. The potential of the anode 3 during the time that the grid II! is at zero potential is such that the control electrode II 4 of tube I09 (which is connected to anode II3) will permit no current to flow to the anode I I5 because of the presence of resistance II6. During this time the cathode ray beam is being deflected and is producing the characteristic curve, but when condenser 38 has been fully charged and begins to discharge through the tube 36, the control electrode H2 of tube I08 is made more negative with the result that current flow to the anode H3 is diminished or interrupted. Because oi the decrease in the potential drop across the resistance I I8 the potential or the control grid II! or the tube I09 is permitted to increase positively, with the result that the conductivity of this triode and the accompanying anode current substantially short-circuits the output from the amplifier tube I02 with the further result that no potential is applied to the vertical deflecting plate IIO. During the horizontal return of the cathode ray beam, there-- fore, the beam is prevented from being deflected vertically and accordingly the return trace of the cathode ray beam does not interfere with the characteristic curve already produced by the cathode ray beam.

In order that the position of the characteristic curve as produced on the screen of the cathode ray tube may be controlled, means are provided for biasing the horizontal and vertical deflecting plates and additional means are provided for positioning the zero setting of the system and the zero adjustment of the oscillator. when it is desired to performv this adjustment the switch 52 is closed, placing the small condenser 60 in parallel with the resistance 46. In order that the operation of this portion of the system may be entirely understood, values will be as signed to various of the elements which are eflective in this system and it is to be understood that these values are merely taken by way of example, and that they may be changed to suit the particular requirements of the system. Assume that the value of the condenser 38 is I5 microfarads, the charging rate of which is determined by the size of the resistance 40 as stated above.

Assume also that the value of the resistance 48 is 500 ohms, the value of resistance 46 is 50,000 ohms and the value of the condenser 50 is .001 microtarad. During the charging of the condenser 38 no current is present in the anode circuit of the tube 36 and accordingly no charge will be accumulated on the condenser 50. When the condenser 38 has acquired a predetermined charge the tube 36 will begin to conduct and accordingly begin to discharge the condenser 38. As soon as this operation begins current flows in the anode circuit of tube 36 with the result that the very small condenser 50 will be immediately charged and this charge will so reduce the potential existing at the anode of tube 36 that the tube will again become non-conductive.

In view of the relative sizes of the condensers 38 and 50, very little of the accumulated charge on the condenser 38 will be removed to completely charge condenser 50. After the condenser 50 has been charged, and the tube 36 has again been blocked, the condenser 50 will discharge through' the resistance 46, the rate of discharge being determined by the value of the resistance.

During the time when the small condenser 50 is discharging, the large condenser 38 will again be charged by an amount equal to the amount of the charge which was removed from it by the previous charging of condenser 50. As soon as the condenser 50 has discharged, the tube 36 will again become conductive, and the cycle will again be repeated. This cycle of operation may have a frequency of the order of several kilocycles, and so long as the switch 52 remains closed the condenser 38 cannot discharge with the result that the system is maintained at a 52 is then opened and the oscillator I is permitted to operate in the usual manner.

In order that a cathode ray beam may be developed in the cathode ray tube 30 appropriate potentials must of course be applied to the elements of the cathode ray gun structure in a. manner well knownin the art. In order that the position ofthe characteristic curve may be positioned vertically and horizontally on the fluorescent screen of the cathode ray tube means are provided whereby biasing potentials may be applied to the horizontal and vertical deflecting plates. A source ofpositive potential I20'is provided and a high resistance I22 is connected between this source of current and ground. The second anode of the cathode ray tube and one of each of the horizontal and vertical deflecting plates are connected together and are in turn connected to an adjustable point along the resistance I22. The operation of this portion of the system is believed to be clear to those skilled in the art and a further explanation is believed to be unnecessary.

In order that the beam may be focused a resistance I23 is provided between a negative source of current I24 and ground. The first anode of the cathode ray tube is adjustably connected to this resistor and by moving the adjustable point along the resistor the potential applied to the first anode may be controlled which, of which, controls the focus of the beam in a manner well known in the art. It might be mentioned that the bias adjustment to the deflecting plates must be made first, since the second anode potential is controlled thereby, and then the .focus adjustment may be made.

From the above it may be seen therefore that cyclically varying frequencies may be produced, the oscillations beginning at or about 15,000 cycles per second and decreasing to a value at or about 20 cycles per second. These frequencies are applied toa frequency discriminating network to produce horizontal deflection of a cathode ray beam, which in this particular instance is from left to right on the viewing screen of the cathode ray tube, the deflection being purely logarithmic or being expanded in certain portions of the frequency range at the choice of the operator. The cyclically varying frequencies are also applied to apparatus under test, the output from which is applied to the vertical deflecting plates of the cathode ray tube, with the result that a frequency response characteristic curve of the particular apparatus under test may be presented on the viewing screen of the cathode ray tube.

In Figure 3 is shown a plurality of curves representing the horizontal deflection as the ordinate and as a function of the frequency in cycles per second which are applied to the frequency responsive network 24. The broken curve I25 represents the deflection of the cathode ray beam *when the beam is deflected horizontally logalogarithmic in nature.

whereby expansion within particular frequency ranges may be accomplished it is of course understood that a greater number of contacts may be used with a corresponding number of condensers connected thereto in order that a greater number of expansible frequency ranges may be selected.

If, for instance, a condenser and resistance of such magnitude are used as to produce a frequency band expansion corresponding to that indicated by curve I26, then the response of the particular apparatus being tested will be shown in considerable detail within the limits of approximately 40 cycles and700 cycles per second.

If it is desired, however, to accurately determine the frequency'response of the particular apparatus under test, then only the straight line portion of the particular curve should be used and in that event, the curve represented at I26 would show accurately the frequency response of the apparatus between approximately 100 and 500 cycles per second. This range of frequencies would occupy over half of the horizontal width of the produced image of the cathode ray tube. By

selecting different condenser and resistance combinations various other bands within the frequency range of the apparatus may be expanded in order that the response characteristics within the particular selected band may be more accurately determined. Ordinarily, however, one curve of frequency response is made using straight logarithmic deflection without any expansion by placing the switch arm on contact 12 and then a series of other curves are produced by expanding particular frequency ranges over the entire frequency range of the system.

Figures 4, 5, 6 and? show, by way of example, the results which may be produced by the present invention and the curves shown in these figures were made from actual photographs taken of the curve as it appeared on the fluorescent screen of a cathode ray tube. The curves shown indicate the frequency response of a 12 inch speaker with a baifle 2 ft. square and open on three sides and the back. The microphone for picking up the sound produced by the speaker was positioned at a distance of 6 inches from the speaker. The apparatus was not positioned in an acoustically designed room, and the curves are not for the purpose of indicating the true performance and fidelity of the speaker under ideal conditions, but are for indicating the results which may be obtained through the use of the present invention. A horizontal sweep of twenty seconds time duration was used for each curve but more detail could be had by increasing the time to about one minute. In Figure l the switch arm 10 was placed on contact I2 and the horizontal deflection of the cathode ray beam was accordingly It may be seen from Figure 4 that the speaker was relatively insensitive to 50 cycles per second but that the sensitivity raised very rapidly and in fact was somewhatpeaked at around 100 cycles. The sensitivity then reducedsomewhat and continued with varying degrees of sensitivity to a frequency of about 5,000 cycles at which time the response diminished rapidly with a slight peak between 10,000 and 15,000.

In order that the response of the speaker over particular frequency bands within the range of the test apparatus could be more accurately ascertained, portions of the frequency band were expanded. In Figure is shown an expansion with respect to frequency in the range' between 50 and 100 cycles per second. The peak A which occurs at about 100 cycles in Figure 4 may again be seen in Figure 5 and the small ripple at about 200 cycles in Figure 4 is much more clearly seen in Figure 5.

Figure 6 shows an expansion in the frequency range between 100 and 1000 cycles per second. Here, peaks marked B through F in Figure 4 may be more clearly seen and are shown in more detail in Figure 6.

Figure 7 shows a test of the same speaker wherein the frequency range between 1000 and 5000 was expanded and the points of the curve marked G, H, K, L, M and N in Figure 4 are clearly shown in detail in Figure 7. Attention is particularly directed to the small loops M and N in Figure 1, which, when expanded, occupy considerable lateral space in Figure 7. It may be seen that the loop M is in face made up of a plurality of superimposed small variations in frequency response which do not appear in Figure 4.

While the curves shown in Figure 4 through 7 were made from a loud speaker as the apparatus tested, it is to be understood that any other electrical apparatus which is designed to respond to different frequencies in any particular manner may be tested. Furthermore, the apparatus may also be used to test mechanical devices, the device being subjected to vibrations in accordance with the varying frequencies and the response of the apparatus being translated into potential variations by means of a piezo-electric crystal or some other element which will produce electrical variations from changes in mechanical stress.

It is also to be understood that although speciiic tubes are designated as applicable in the present invention, other tubes may well be used provided the function of the tubes will correspond to that required by the particular portion of the circuit wherein the tube is used.

It is also to be understood that the curve is best seen on the cathode ray tube if the tube is provided with a screen having a long persistency although this is not entirely necessary, particularly when the characteristic curve is to be photographed.

Other. alterations and modifications may be made in the present invention without departing from the spirit and scope thereof, and it is desired that any and all such modifications be considered as being within the purview of the present invention except as limited by the hereinafter appended claims.

Iclaim:

1. A relaxation oscillator comprising a condenser, a resistance, means for charging said condenser through said resistance, means for discharging said condenser comprising an electron discharge device having an electron emitter, a control electrode and and an anode, means for connecting the electron emitter to one terminal of said condenser, means including another resistance for connecting the anode to 'the other terminal of said condenser, a relatively small condenser, and means whereby said last named condenser may be selectively connected in parallel with a substantial portion of said another resistance.

2. A relaxation oscillator comprising a condenser, a resistance, means for linearly charging said condenser through said resistance, means for substantially instantaneously discharging said condenser comprising an electron discharge device having a cathode, a control electrode and an anode, means for connecting the cathode to one terminal of said condenser, means including a second resistance for connecting said anode to the other terminal of said condenser, a relatively small condenser, and means for selectively connecting said last named condenser in parallel with a substantial portion of said second resistance.

3. A relaxation oscillator comprising acondenser, an impedance, means for charging said condenser through said impedance at a constant rate, means for periodically discharging said condenser comprising an electron discharge device having an electron emitter, a control electrode and an anode, means for connecting the electron emitter to one terminal of said condenser, means for connecting said anode to the other terminal,

of said condenser, said last named means including a resistance, a relatively small condenser, and means whereby the last named condenser may be selectively connected in parallel with a portion of said last named resistance.

4. A relaxation oscillation generator, comprising 5. A relaxation oscillation generator comprising a condenser, a resistance, a source of potential for substantially linearly charging. saidv condenser through said resistance, means for substantially instantaneously discharging said condenser comprising a gas discharge tube, a second resistance, means for connecting said discharge tube, said second resistance and said condenser in series, and means for connecting a relatively small condenser across a substantial portion of said second resistance whereby complete discharge of said first named condenser may be prevented.

6. A relaxation oscillation generator comprising a condenser, a resistance connected in series therewith, means for charging said condenser through said resistance at a constant rate, means for periodically discharging said condenser comprising an ionizable discharge tube, a second resistance, means for connecting said discharge tube, said second resistance and'said condenser in a series circuit, a relatively small condenser, and switch means whereby said last named condenser may be selectively connected across a portion of said second resistance whereby appreciable discharge of said first named condenser may be prevented.

7. A relaxation oscillation generator comprising a condenser, a resistance and a source of potential connected acrosssaid condenser whereby said condenser may be charged at a rate determined by the value of said resistance, means for discharging said condenser comprising a discharge tube having a cathode, a control electrode and an anode, means for maintaining said control electrode negative with respect to said cathode, means for connecting the cathode of said discharge tube to one terminal of said condenser, means including a second resistance for connecting the anode of said tube to the other terminal of said condenser, and means for con necting a relatively small condenser in parallel with a substantial portion of said second resistance whereby the discharge of said first condenser by said tube may be prevented.

8. A relaxation oscillation generator comprising a condenser, a resistance and a source of potential connected across said condenser whereby said condenser may be charged at a substantially constant rate determined by the value of said resistance, means for periodically discharging said condenser comprising a gas discharge tube having a cathode, a control electrode and an anode, means for maintaining said control electrode negative with respect to said cathode, means for connecting the cathode of said discharge tube to one terminal of said condenser, means including a second resistance for connecting the anode of said tube to the other terminal of said condenser, and means for selectively connecting a relatively small condenser in parallel with a portion of said second resistance whereby complete discharge of said first condenser by said tube may be prevented.

9. A relaxation oscillation generator comprising a condenser, means for charging said condenser at a relatively slow rate, means for substantially discharging said condenser comprising a discharge tube having a cathode, a control electrode and an anode, means for connecting said cathode to one terminal. of said condenser, means for maintaining said control electrode normally negative with respect to said cathode, means including a resistance for connecting said anode to the other terminal of said condenser, means to prevent a substantial discharge of said condenser by said tube including a relatively small condenser, and means for selectively connecting said last named condenser across a substantial portion of said resistance whereby when said last named condenser is present in,the circult, the discharge tube will be caused to operate at a very high rate and said first named condenser will remain substantially completely charged.

10. A relaxation oscillation generator comprising a condenser, means for charging said condenser at a relatively uniform slow rate, means for substantially instantaneously discharging said condenser comprising a gas discharge tube having a cathode, a control electrode and an anode. means for maintaining said control electrode negative with respect to saidcathode, means for connecting said cathode to one terminal of said condenser, means including a resistance for connecting said anode to the other terminal 01' said condenser, means to prevent the complete discharge of said condenser by said tube including a condenser, and means for selectively connecting said last named condenser across a portion of said resistance whereby when said last named condenser is present in the circuit, the discharge tube will be caused to operate at a very high rate and said first named condenser will remain substantially completely charged.

11. A relaxation oscillation generator comprising a condenser, means for charging said condenser at a uniform slow rate, means for rapidly discharging said condenser comprising a gas discharge tube having a cathode, a control electrode and an anode, means for connecting said cathode to one terminal of said condenser, means for maintaining said control electrode negativewith respect to said cathode, means including a resistance for connecting said anode to the other terminal of said condenser, and means for selectively connecting a relatively small condenser across a substantial portion of said resistance whereby when said last named condenser is present in the circuit, the discharge tube will be caused to operate at a very high rate and said first named condenser will remain substantially completely charged.

JESSE B. SHERMAN. 

